Extrusion apparatus and method with pressure equalization

Abstract

An extrusion apparatus and method for producing a composite profile strip characterized by an extrusion head having plural flow channels extending to an extrusion die and at least two extruders for feeding respective components at respective different pressures into the flow channels for passage to the extrusion die. The extrusion die has a common die outlet from which the components are discharged to form the composite profile strip, and respective flow restriction devices are disposed in the flow channels between the extruders and the extrusion die. The flow restriction devices are operative to decrease the difference in pressure between the components before being brought together at the extrusion the extrusion die and further to dampen the effect changes in extruder speed has on the profile of the composite profile strip.

What is claimed is: 
     
       1. An extrusion apparatus for producing a composite profile strip, comprising an extrusion head having plural flow channels extending to an extrusion die, at least two extruders for feeding respective components at respective different pressures into said flow channels for passage to said extrusion die, said extrusion die having a common die outlet from which the components are discharged to form the composite profile strip, and respective flow restriction devices disposed in said flow channels between said extruders and said extrusion die, said flow restriction devices being operative to decrease the difference in pressure between the components at the extrusion die to about 250 psi or less prior to the components being brought together. 
     
     
       2. An extrusion apparatus as set forth in claim 1, wherein said flow restriction devices are removably disposed in said flow channels. 
     
     
       3. An extrusion apparatus as set forth in claim 1, further comprising pressure sensors associated with said flow channels which sense the pressures of the components downstream of the flow restriction devices, and a controller which controls the speeds of said extruders in response to outputs of said pressure sensors. 
     
     
       4. An extrusion apparatus as set forth in claim 1, wherein at least one of said flow restriction devices includes a foraminous member. 
     
     
       5. An extrusion apparatus as set forth in claim 4, wherein said foraminous member includes a screen. 
     
     
       6. An extrusion apparatus as set forth in claim 5, wherein said foraminous member includes a perforated plate backing said screen. 
     
     
       7. An extrusion apparatus as set forth in claim 4, wherein said foraminous member includes a perforated plate. 
     
     
       8. An extrusion apparatus as set forth in claim 1, wherein the flow restriction devices are operative to reduce the difference in pressure to about 200 psi or less prior to the components being brought together. 
     
     
       9. A method of extruding a composite profile strip comprising the steps of supplying components at respective different pressures to respective flow channels in an extrusion head for passage to an extrusion die that has a common die outlet from which the components are discharged to form the composite profile strip, and causing the components to flow through respective flow restriction devices prior to passage to the extrusion die for reducing the difference in pressure between the components to about 250 psi or less before being brought together at the extrusion die. 
     
     
       10. A method as set forth in claim 9, including the step of monitoring the pressures of the components downstream of the flow restriction devices, and controlling the speeds of said extruders in response to the sensed pressures. 
     
     
       11. A method as set forth in claim 9, wherein at least one of the flow restriction devices includes a foraminous member. 
     
     
       12. A method as set forth in claim 11, wherein a screen is used as the foraminous member. 
     
     
       13. A method as set forth in claim 12, wherein said foraminous member includes a perforated plate backing said screen. 
     
     
       14. A method as set forth in claim 11, wherein said foraminous member includes a perforated plate. 
     
     
       15. A method as set forth in claim 9, wherein the flow restriction devices reduce the difference in pressure to about 200 psi or less prior to the components being brought together. 
     
     
       16. A method of extruding a composite profile strip at different speeds comprising the steps of using at least two extruders to feed components at respective different pressures to respective flow channels in an extrusion head for passage to an extrusion die that has a common die outlet from which the components are discharged to form the composite profile strip at a first speed, and selecting and positioning flow restriction devices in the flow channels to reduce the difference in pressures of the components to about 250 psi or less prior to passage to the extrusion die. 
     
     
       17. A method as set forth in claim 16, comprising the step of varying the speed of the extruders to change the speed at which the composite profile strip is discharged from the extrusion die, while the respective flow restriction devices in the flow channels function dampen the effect the extruder speed change has on the profile of the composite profile strip. 
     
     
       18. A method as set forth in claim 16, wherein said selecting and positioning step includes selecting a screen mesh size for each flow restriction device to provide a pressure drop greater for the higher pressure feed than the lower pressure feed. 
     
     
       19. A method as set forth in claim 16, wherein the flow restriction devices are selected to reduct the difference in pressure to about 200 psi or less prior to the components being brought together.